1. Field of the Invention
The present invention relates to an apparatus and method thereof for inspecting optical members, mostly optical members made of plastic, and more particularly relates to an apparatus and method for inspecting optical members using image processing technology.
2. Description of the Related Art
Recently, optical members made of plastic have been widely used in photographing lens systems or finders of cameras, due to their lightweight and low-cost qualities.
However, with such optical members there is a possibility that dust, e.g., in the form of carbonated plastic, remains in the mold after injection molding and thus might enter inside a lens being molded. Additionally, since plastic is softer than glass, there is a higher possibility of a flawed lens being produced, and therefore inspection for defects before assemble has an increased importance.
Defect inspection is undertaken in order to judge whether an optical member has sufficient performance to be used, namely whether it is non-defective and useable, or is defective and can not be used.
In the prior art, defect inspection is usually either in the form of visual inspection by the naked eye, in which a skilled worker illuminates the optical member, such as a lens or prism, by an intense light, or in the form of image processing of an inputted image obtained by picking-up an image of the optical member.
If dust has entered a lens, factors such as the size of the dust, the depth of entry, or the distance from the optical axis, need to be determined. On the other hand, if there is a flaw, factors such as the size of the flaw, the surface on which the flaw is, or the distance of the flaw from the optical axis, need to be determined.
The criteria used for judging whether an optical member is defective or non-defective, is different depending on whether dust has entered the member or whether there is a flaw, for example, even in the case that the dust and the flaw have the same size, one may be allowable, e.g., the dust, while the other type of defect, e.g., the flaw, is not. Therefore, an inspector should judge whether the lens is defective or non-defective, not only from the extent of the defect, but also from the identification of the type of defect, i.e., whether it is dust or a flaw.
In visual inspections by the naked eye, a judgement as to whether a lens is defective or non-defective is subjective according to each individual inspector, and thus judgement criteria may change according to the physical condition of the same inspector, e.g., in the weakening of the eyes, to say nothing of the judgement criteria of a different inspector, thus making it difficult to maintain unitary judgements.